The decline in the atmosphere of an ozone-depleting chemical banned by the Montreal Protocol has recently slowed by half, suggesting a serious violation of the 196-nation treaty, researchers revealed Wednesday.
Measurements at remote sites -- including the government-run Mauna Loa Observatory in Hawaii -- of the chemical, known as CFC-11, point to East Asia as the source or renewed production.
"We show that the rate of decline of atmospheric CFC-11 was constant from 2002 to 2012, and then slowed by about 50 percent after 2012," an international team of scientists concluded in a study.
"This evidence strongly suggests increased CFC-11 emissions from eastern Asia after 2012."
The ozone layer in the stratosphere, 10-to-40 kilometres (6-25 miles) above Earth's surface, protects life on the planet from deadly ultraviolet radiation.
The 1987 Montreal Protocol banned industrial aerosols such as chlorofluorocarbons (CFCs) that were chemically dissolving ozone, especially above Antarctica.
At its most depleted, around the turn of the 21st century, the ozone layer had declined by about five percent. Today, the "hole in the ozone" over the South Pole is showing clear signs of recovery.
"The ozone layer remains on track to recovery by mid-century," the UN Environment Programme (UNEP) said in a statement, reacting to the findings.
But "continued increase in global CFC-11 emissions will put that progress at risk."
Widely used in 1970s and 1980s as propellant in aerosol sprays, as well as in refrigeration and air conditioning systems, CFCs do not exist in nature.
Other scientists not involved in the study signalled its importance.
"This is atmospheric detective work at its finest," said Piers Forester, head of the Priestley International Centre for Climate at the University of Leeds.
“The authors pinpoint a new source of CFC-11 to East Asia, breaking Montreal Protocol rules."